Generally, an electrical appliance such as a washing machine has a control panel with one or more control switches. By operating the control switches, desired operating conditions of the electrical appliance are adjusted. FIG. 1 is a schematic view illustrating a control panel and some rotary control switches of a washing machine according to the prior art. As shown in FIG. 1, the control panel 2 of the washing machine 1 is a circuit board. Several rotary control switches 20 are mounted on the control panel 2. For clarification, three rotary control switches 20a, 20b and 20c are shown in the drawings and the upper cover for sheltering the control panel 2 is exempted. By rotating the rotary control switches 20a, 20b and 20c, desired operating conditions (e.g. the motor's speed) of the electrical appliance are adjusted.
FIG. 2A is a schematic exploded view illustrating a rotary control switch of the control panel as shown in FIG. 1. Take the rotary control switch 20a for example. As shown in FIG. 2A, the rotary control switch 20a includes a body member 21, a shaft member 22 and a conducting member 23. FIG. 2B is a schematic rear view illustrating the body member of the rotary control switch of FIG. 2A. Please refer to FIGS. 2A and 2B. A receptacle 210 is defined at the rear side of the body member 21. The receptacle 210 includes a first receiving part 2101 and a second receiving part 2102. Several recesses 211 are formed in the sidewall of the first receiving part 2101. The bulk of the second receiving part 2102 is greater than that of the first receiving part 2101. The body member 21 further includes a perforation 212 and several posts 213. The perforation 212 runs through the body member 21 and is communicated with the receptacle 210. The posts 213 are vertically extended from the bottom surface of the body member 21 for facilitating fixing the rotary control switch 20a on the control panel (as shown in FIG. 1).
The shaft member 22 includes a base 220 and a rotating shaft 221. The base 220 includes a first base segment 2201 and a second base segment 2202. The first base segment 2201 is disposed on the second base segment 2202. In addition, a receiving hole 222 is formed in an outer periphery of the first base segment 2201 for receiving therein a sustaining structure 225 that is collectively defined by a resilient element 223 and a sustaining element 224. The rotating shaft 221 is extended vertically and upwardly from the first base segment 2201 such that the rotating shaft 221 is perpendicular to the receiving hole 222.
The conducting member 23 is substantially a metallic plate with several pins 230 and several apertures 231. The apertures 231 are aligned with corresponding protrusions (not shown) on the bottom surface of the second base segment 2202 of the base 220. After the protrusions are inserted into the apertures 231, the conducting member 23 may be fixed on the bottom surface of the second base segment 2202 of the base 220. After the rotating shaft 221 is penetrated through the perforation 212 of the body member 21, the first base segment 2201 and the second base segment 2202 are respectively accommodated within the first receiving part 2101 and the second receiving part 2102 of the receptacle 210 of the body member 21. At the same time, the sustaining structure 225 that is perpendicular to the rotating shaft 221 is sustained against a recess 211 in the sidewall of the first receiving part 2101. After the posts 213 of the body member 21 are inserted into corresponding insertion holes 24 of the control panel 2, the rotary control switch 20a is fixed on the control panel 2 (as shown in FIG. 1).
Please refer to FIG. 1 again. The control panel 2 has several conducting regions 25. For example, corresponding to the rotary control switches 20a, 20b and 20c, the control panel 2 has three conducting regions 25a, 25b and 25c, respectively. Take the conducting region 25a for example. The conducting region 25a has several contact pads 250. The contact pads 250 include a first conducting piece 251 and several second conducting pieces 252 that enclose the first conducting piece 251. The insertion holes 24 are disposed in the vicinity of the conducting region 25a. After the rotary control switch 20a is fixed on the control panel 2 by inserting the posts 213 of the body member 21 into corresponding insertion holes 24 of the control panel 2, the rotary control switch 20a is mounted over the conducting region 25a. Meanwhile, the pins 230 of the conducting member 23, which are attached on the bottom surface of the second base segment 2202 of the shaft member 22, are contacted with corresponding contact pads 250. When an external force is exerted on the rotating shaft 221 of the rotary control switch 20a, the base 220 is rotated with the rotating shaft 221. As the base 220 is rotated from a first position to a second position, the sustaining structure 225 is disengaged from a first recess 211 and then engaged with a second recess 211. In addition, the pins 230 of the conducting member 23 are contacted with other contact pads 250. Under this circumstance, an operating condition (e.g. a motor's speed) of the washing machine 1 is selected. The relation between the rotary control switch 20b and the conducting region 25b and the relation between the rotary control switch 20c and the conducting region 25c are similar to the relation between the rotary control switch 20a and the conducting region 25a. 
The conventional rotary control switch 20, however, still has some drawbacks. For combining the shaft member 22 with the body member 21, a sharp tool is required to manually push the sustaining structure 225 toward the receiving hole 222 in order to successfully accommodate the first base segment 2201 of the base 220 within the first receiving part 2101 of the receptacle 210, because the sustaining structure 225 is laterally protruded from the first base segment 2201 of the base 220. In addition, for mounting the combination of the body member 21 and the shaft member 22 on the control panel 2, a plastic tube 26 is sheathed around the body member 21 and the shaft member 22 to temporarily combine the body member 21 and the shaft member 22 together. The use of the plastic tube 26 increases extra cost. Moreover, for overcoming a short-circuit problem of the conducting member 23 or the control panel 2, a waterproof glue is usually applied on the junction between the rotary control switch 20 and the control panel 2 to prevent moist gas or vapor gas from entering the rotary control switch 20. In other words, the process of assembling the conventional rotary control switch 20 is very troublesome and complicated.
Moreover, the rotary control switches 20a, 20b and 20c need to be respectively mounted on the conducting regions 25a, 25b and 25c. The circuitry layout of the conducting regions 25a, 25b and 25c are different. If a rotary control switch is erroneously mounted on the proper conducting region, the user fails to control the operating conditions of the washing machine 1 by using the rotary control switch 20 and the control panel 2. Moreover, since a large-area body member 21 is used for facilitating firmly fixing the rotary control switch 20 on the control panel 2, the space utilization of the control panel 2 is limited.
There is a need of a providing an improved rotary control switch to obviate the drawbacks encountered from the prior art.